Synthesis, x-ray crystal structure, and magnetic properties of two dinuclear manganese(II) compounds containing nitronyl nitroxides, imino nitroxides, and their reduced derivatives

The nitronyl nitroxide 2-phenyl-4,4,5,5-tetramethyl-4,5-dihydr1oH- -imidazolyl- 1- oxy 3-oxide (NITPh) is reduced in the reaction with manganese(I1) hexafluoroacetylacetonate (Mn(hfac),) to yield l-hydroxy-2-phenyl-4,4,5,5-tetramethyl-4,5-dihydro-l~- imidazole (IMHPh). A solid compound of formula [Mn(hfac),(IMHPh)],(NITPh) (I) is obtained, whose crystal structure was determined through X-ray diffraction. I crystallizes in the triclinic Pi space group: a = 13.566 (2) A, b = 15.079 (3) A, c = 21.622 (4) A, a = 68.36 (2)O, /3 = 77.18 ( 2 ) O , y = 61.47 (2)O, 2 = 2. A similar behavior was observed with the imino nitroxide 2-phenyl-4,4,5,5-tetramethyl-4,5-dihydro-l~-imidazolyl-l-ox(yI MPh) and Mn(hfa~)~.2H,OI. n this case a solid compound of formula Mn(hfac) (IMHPh)(IMPh) (11) is obtained, which crystallizes in the monoclinic space group P2,/c: a = 13.391 (2) A, b = 22.725 (3) 1, c = 14.987 (2) A, /3 = 66.73 (2)O, 2 = 4. The crystal structure of I consists of two different centrosymmetric units, of formulas [Mn(hfac),(IMHPh)(NITPh)], and [Mn(hfac),(IMHPh)],, respectively. The reduced form of the radical bridges the manganese(I1) ions in both units, and in the former, a molecule of radical is hydrogen bonded to its reduced form. The crystal structure of I1 consists of centrosymmetric units [Mn(hfac),(IMHPh)(IMPh)], with a geometry similar to that of the corresponding unit of I. The magnetic properties of both I and I1 were studied in the range 5-300 K, showing that the manganese ions are weakly coupled in an antiferromagnetic fashion. The EPR spectra were attributed to the coupled S = 5 state.